1. Field of the Invention
The present invention relates to a positive photoresist composition that is excellent in properties as a resist (resist properties) such as sensitivity, definition, focal depth range properties (depth of focus; DOF), exposure margin, and density-dependent variations in size and is particularly useful in the formation of ultrafine resist patterns of not more than 0.35 xcexcm.
2. Description of the Related Art
Certain positive photoresist compositions containing an alkali-soluble novolak resin and a non-benzophenone naphthoquinonediazido-group-containing compound (photosensitizer) have been proposed as photoresist materials that can form ultrafine resist patterns of not more than half a micron and particularly of not more than 0.35 xcexcm in photolithography using i-line (365 nm).
Among such photosensitizers, esters (quinonediazide esters) of a low-molecular phenolic compound having a xe2x80x9clinearxe2x80x9d phenol skeleton comprising combined four to seven benzene rings with a 1,2-naphthoquinonediazidosulfonic acid compound have been reported as photosensitizers having a high definition (e.g., Japanese Patent Laid-Open Nos. 6-167805; 7-152152; 7-159990; 7-168355; 8-129255; 8-245461; 8-339079; 9-114093; 12-29208; and 12-29209).
However, a demand has been made on positive photoresist compositions that have further excellent resist properties such as sensitivity, definition, focal depth range properties, and exposure margin in the formation of ultrafine resist patterns of not more than 0.35 xcexcm, smaller than the wavelength of i-line (365 nm).
In the manufacture of logic integrated circuits (logic ICs) comprising a mixture of regular, dense patterns such as line-and-space (LandS) patterns and irregular, isolation patterns, the positive photoresist composition must form resist patterns with less xe2x80x9cdensity-dependent variations in sizexe2x80x9d, i.e., must form such dense patterns and isolation patterns in exact accordance with set dimensions with a good shape under the same exposure conditions.
In this connection, certain photolithographic techniques using short-wavelength light sources such as KrF (248 nm) and ArF (193 nm) have been proposed in the formation of resist patterns of not more than 0.35 xcexcm. However, these techniques require a significant capital investment to build plants and equipment in production lines using these light sources, and the capital investment cannot be recovered. Accordingly, the i-line (365 nm) photolithographic process, which is now mainstream, must be employed for some time in the future.
Accordingly, it is an object of the present invention to provide a positive photoresist composition that can yield ultrafine resist patterns of not more than half a micron, particularly of not more than 0.35 xcexcm in photolithography using i-line (365 nm) and is excellent in resist properties such as sensitivity, definition, focal depth range properties (DOF), exposure margin, and density-dependent variations in size.
After intensive investigations to achieve the above objects, the present inventors have found that a positive photoresist composition including an alkali-soluble resin and a mixture of specific quinonediazide esters (photosensitizers) can yield resist patterns with satisfactory resist properties such as sensitivity, definition, focal depth range properties (DOF), exposure margin, and density-dependent variations in size even in the formation of ultrafine resist patterns of not more than 0.35 xcexcm, smaller than the wavelength of i-line (365 nm). The present invention has been accomplished based on these findings.
Specifically, the present invention provides a positive photoresist composition including (A) an alkali-soluble resin ingredient; and (B) a quinonediazide ester ingredient, in which the ingredient (B) includes (b1) a quinonediazide ester represented by following Formula (I): 
wherein each of Ds is independently a hydrogen atom or a 1,2-naphthoquinonediazido-5-sulfonyl group, where at least one of Ds is a 1,2-naphthoquinonediazido-5-sulfonyl group; and (b2) a quinonediazide ester, other than the quinonediazide ester (b1), represented by following Formula (II): 
wherein each of R1, R2, R3, R4, R5, R6, R7, and R8 is independently a hydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkyl group containing 3 to 6 carbon atoms;
each of R9, R10, and R11 is independently a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms;
Q is a hydrogen atom or an alkyl group containing 1 to 6 carbon atoms, or Q is combined with R9 to form a cycloalkyl group containing 3 to 6 carbon members or a residue represented by following Formula (III): 
wherein each of R12 and R13 is independently a hydrogen atom, a halogen atom, an alkyl group containing 1 to 6 carbon atoms, an alkoxy group containing 1 to 6 carbon atoms, or a cycloalkyl group containing 3 to 6 carbon atoms; and
c is an integer from 1 to 3;
each of Ds is independently a hydrogen atom or a 1,2-naphthoquinonediazido-5-sulfonyl group, where at least one of Ds is a 1,2-naphthoquinonediazido-5-sulfonyl group;
each of a and b is independently an integer from 1 to 3;
d is an integer from 0 to 3; and
n is an integer from 0 to 3,
wherein, when n is 0, Q is the residue represented by Formula (III) or is combined with R9 to form a cycloalkyl group containing 3 to 6 carbon atoms.
The positive photoresist composition may further include (C) an alkali-soluble low-molecular compound having a phenolic hydroxyl group and having a molecular weight less than or equal to 1000.
The quinonediazide ester (b2) is preferably a quinonediazide ester represented by following Formula (IV): 
wherein D, R1 to R6, R12, R13, a, b and c have the same meanings as defined above.
The ratio of the quinonediazide ester (b2) to the quinonediazide ester (b1) in the ingredient (B) is preferably from 10% to 200% by weight.
The positive photoresist compositions of the present invention can yield ultrafine resist patterns of not more than half a micron, particularly of not more than 0.35 xcexcm, and are excellent in resist properties such as sensitivity, definition, focal depth range properties (DOF), exposure margin, and density-dependent variations in size in photolithography using i-line (365 nm).
Ingredient (A): Alkali-Soluble Resins
Alkali-soluble resins for use as the ingredient (A) in the present invention are not specifically limited and can be freely chosen from those conventionally used as film-forming substances in positive photoresist compositions. Among them, preferred alkali soluble resins are condensates of aromatic hydroxy compounds with aldehydes and/or ketones, as well as polyhydroxystyrenes and derivatives thereof.
Such aromatic hydroxy compounds include, but are not limited to, phenol; m-cresol, p-cresol, o-cresol; 2,3-xylenol, 2,5-xylenol, 3,5-xylenol, 3,4-xylenol, and other xylenols; m-ethylphenol, p-ethylphenol, o-ethylphenol, 2,3,5-trimethylphenol, 2,3,5-triethylphenol, 4-tert-butylphenol, 3-tert-butylphenol, 2-tert-butylphenol, 2-tert-butyl-4-methylphenol, 2-tert-butyl-5-methylphenol, and other alkyl-substituted phenols; p-methoxyphenol, m-methoxyphenol, p-ethoxyphenol, m-ethoxyphenol, p-propoxyphenol, m-propoxyphenol, and other alkoxy-substituted phenols; o-isopropenylphenol, p-isopropenylphenol, 2-methyl-4-isopropenylphenol, 2-ethyl-4-isopropenylphenol, and other isopropenyl-substituted phenols; phenylphenol, and other aryl-substituted phenols; 4,4xe2x80x2-dihydroxybiphenyl, bisphenol A, resorcinol, hydroquinone, pyrogallol, and other polyhydroxyphenols. Each of these compounds can be used alone or in combination.
The aldehydes include, but are not limited to, formaldehyde, paraformaldehyde, trioxane, acetaldehyde, propionaldehyde, butyraldehyde, trimethylacetaldehyde, acrolein (acrylaldehyde), crotonaldehyde, cyclohexanecarbaldehyde, furfural, furylacrolein, benzaldehyde, terephthalaldehyde, phenylacetaldehyde, xcex1-phenylpropylaldehyde, P-phenylpropylaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, o-chlorobenzaldehydie, m-chlorobenzaldehyde, p-chlorobenzaldehyde, and cinnamaldehyde. Each of these aldehydes can be used alone or in combination. Among these aldehydes, formaldehyde is preferred for its high availability. To improve thermal resistance of the positive photoresist compositions, a combination use of a hydroxybenzaldehyde and formaldehyde is typically preferred.
The ketones include, but are not limited to, acetone, methyl ethyl ketone, diethyl ketone, and diphenyl ketone. Each of these ketones can be used alone or in combination. An appropriate combination use of an aldehyde with a ketone is also acceptable.
The condensates of aromatic hydroxy compounds with aldehydes and/or ketones can be prepared according to a conventional procedure in the presence of an acidic catalyst. Such acidic catalysts include, but are not limited to, hydrochloric acid, sulfuric acid, formic acid, oxalic acid, and p-toluenesulfonic acid.
The polyhydroxystyrenes and derivatives thereof include, but are not limited to, vinylphenol homopolymers, and copolymers of vinylphenol and a copolymerizable comonomer. Such comonomers include, for example, acrylic acid derivatives, acrylonitrile, methacrylic acid derivatives, methacrylonitrile, styrene, a-methylstyrene, p-methylstyrene, o-methylstyrene, p-methoxystyrene, p-chlorostyrene, and other styrene derivatives.
Of these alkali-soluble resins for use in the present invention as the ingredient (A), preferred resins are alkali-soluble novolak resins having a weight average molecular weight (Mw) from 2000 to 20000, and more preferably from 3000 to 12000. Among them, alkali-soluble novolak resins prepared by condensation of m-cresol and p-cresol with formaldehyde and those prepared by condensation of m-cresol, p-cresol and 2,5-xylenol with formaldehyde are typically preferred for the preparation of positive photoresist compositions having a high sensitivity and a wide exposure margin.
Ingredient (B): Quinonediazide Esters
By using the quinonediazide ester (b1) represented by Formula (I) and the quinonediazide ester (b2) represented by Formula (II) in combination according to the present invention, resist patterns with the satisfactory resist properties can be formed even in the formation of ultrafine resist patterns of not more than 0.35 xcexcm.
The average esterification percentage of the quinonediazide ester (b1) is preferably from 40% to 90% and more preferably from 45% to 75%. If the average esterification percentage is less than 40%, the resulting positive photoresist composition may have a decreased film residual rate and definition, and if it exceeds 90%, the positive photoresist composition may have a decreased sensitivity and may yield increased scum.
The average esterification percentage of the quinonediazide ester (b2) is preferably from 40% to 90% and more preferably from 45% to 75%. If the average esterification percentage is less than 40%, the positive photoresist composition may have a decreased film residual rate and definition, and if it exceeds 90%, the positive photoresist composition may have a decreased sensitivity and may yield increased scum.
Preferred examples of the quinonediazide ester (b2) are quinonediazide esters of:
2,4-bis(3,5-dimethyl-4-hydroxybenzyl)-5-hydroxyphenol, 2,6-bis(2,5-dimethyl-4-hydroxybenzyl)-4-methylphenol, and other linear trinuclear compounds;
bis[2,5-dimethyl-3-(4-hydroxy-5-methylbenzyl)-4-hydroxyphenyl]methane, bis [2,5-dimethyl-3-(4-hydroxybenzyl)-4-hydroxyphenyl]methane, bis[3-(3,5-dimethyl-4-hydroxybenzyl)-4-hydroxy-5-methylphenyl]methane, bis[3-(3,5-dimethyl-4-hydroxybenzyl)-4-hydroxy-5-ethylphenyl]methane, bis[3-(3,5-diethyl-4-hydroxybenzyl)-4-hydroxy-5-methylphenyl]methane, bis[3-(3,5-diethyl-4-hydroxybenzyl)-4-hydroxy-5-ethylphenyl]methane, bis[2-hydroxy-3-(3,5-dimethyl-4-hydroxybenzyl)-5-methylphenyl]methane, bis[2-hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylphenyl]methane, bis[4-hydroxy-3-(2-hydroxy-5-methylbenzyl)-5-methylphenyl]methane, and other linear tetranuclear compounds;
2,4-bis[2-hydroxy-3-(4-hydroxybenzyl)-5-methylbenzyl]-6-cyclohexylphenol, 2,4-bis[4-hydroxy-3-(4-hydroxybenzyl)-5-methylbenzyl]-6-cyclohexylphenol, and other linear pentanuclear compounds; and other linear polyphenol compounds;
tris(4-hydroxyphenyl)methane, bis(4-hydroxy-3,5-dimethylphenyl)-4-hydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-3-hydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-4-hydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-3-hydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-2,4-dihydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-2,4-dihydroxyphenylmethane, bis(4-hydroxyphenyl)-3-methoxy-4-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxyphenyl)-3-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxyphenyl)-2-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxyphenyl)-4-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-2-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-3-hydroxyphenylmethane, bis(3-cyclohexyl-4-hydroxy-6-methylphenyl)-4-hydroxyphenylmethane, bis(3-cyclohexyl-6-hydroxyphenyl)-3-hydroxyphenylmethane, bis(3-cyclohexyl-6-hydroxyphenyl)-4-hydroxyphenylmethane, bis(3-cyclohexyl-6-hydroxyphenyl)-2-hydroxyphenylmethane, bis(3-cyclohexyl-6-hydroxy-4-methylphenyl)-2-hydroxyphenylmethane, bis(3-cyclohexyl-6-hydroxy-4-methylphenyl)-4-hydroxyphenylmethane, bis(3-cyclohexyl-6-hydroxy-4-methylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-2,3,5-trimethylphenyl)-3-hydroxyphenylmethane, bis(4-hydroxy-2,3,5-trimethylphenyl)-4-hydroxyphenylmethane, bis(4-hydroxy-2,3,5-trimethylphenyl)-3,4-dihydroxyphenylmethane, bis(4-hydroxy-2,3,5-trimethylphenyl)-4-hydroxy-3-methoxyphenylmethane, bis(2-methyl-4-hydroxy-5-cyclohexylphenyl)-3,4-dihydroxyphenylmethane, bis(3,5-dimethyl-4-hydroxyphenyl)-2-hydroxyphenylmethane, and other trisphenolic polyphenol compounds. Among them, the quinonediazide esters represented by Formula (IV) are typically preferred.
The ingredient (B) may further comprise additional quinonediazide esters (e.g., those having a benzophenone skeleton) in addition to the quinonediazide esters (b1) and (b2). The amount of such additional quinonediazide esters is preferably less than or equal to 80% by weight and more preferably less than or equal to 50% by weight based on the total weight of the ingredient (B) in order not to adversely affect the advantages of the present invention.
The ratio of the quinonediazide ester (b2) to the quinonediazide ester (b1) is preferably from 10% to 200% by weight and more preferably from 50% to 150% by weight.
If the ratio is less than 10% by weight, the positive photoresist composition may have a deteriorated definition and may yield a resist pattern having an undesired shape. If it exceeds 200% by weight, the positive photoresist composition may have a decreased sensitivity and may often yield increased scum.
The amount of the ingredient (B) in the composition of the present invention is preferably from 10% to 60% by weight and more preferably from 25% to 50% by weight, relative to the total weight of the ingredient (A) and the ingredient (C) added according to necessity. If the amount of the ingredient (B) is excessively small, the positive photoresist composition may not yield images in exact accordance with the pattern and may have deteriorated transfer property. If it is excessively large, the positive photoresist composition may exhibit a decreased sensitivity and definition, and the resulting resist film may have deteriorated uniformity.
Ingredient (C): Sensitizers
For higher sensitivity, the compositions of the present invention preferably further comprise an alkali-soluble low-molecular compound (sensitizer) having a phenolic hydroxyl group and having a molecular weight less than or equal to 1000 as an ingredient (C).
Such ingredients (C) are not specifically limited and include, for example, phenolic compounds conventionally used in positive photoresist compositions for i-line photolithography to improve the sensitivity.
Preferred examples of such phenolic compounds include, but are not limited to, those corresponding to polyphenol compounds of Formula (II) except that all Ds are hydrogen atoms, such as 1-[1,1-bis(4-methylphenyl)ethyl]-4-[1-(4-hydroxyphenyl)isopropyl]benzene, bis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane, 1,4-bis[1-(3,5-dimethyl-4-hydroxyphenyl)isopropyl]benzene, 2,4-bis(3,5-dimethyl-4-hydroxyphenylmethyl)-6-methylphenol, bis(4-hydroxy-3,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-2,5-dimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, 1-[1-(3-methyl-4-hydroxyphenyl)isopropyl]-4-[1,1-bis(3-methyl-4-hydroxyphenyl)ethyl]benzene, 2,6-bis[1-(2,4-dihydroxyphenyl)isopropyl]-4-methylphenol, 4,6-bis[1-(4-hydroxyphenyl)isopropyl]resorcinol, 4,6-bis(3,5-dimethoxy-4-hydroxyphenylmethyl)pyrogallol, 4,6-bis(3,5-dimethyl-4-hydroxyphenylmethyl)pyrogallol, 2,6-bis(3-methyl-4,6-dihydroxyphenylmethyl)-4-methylphenol, 2,6-bis(2,3,4-trihydroxyphenylmethyl)-4-methylphenol, and 1,1-bis(4-hydroxyphenyl)cyclohexane. Among them, typically preferred are 1-[1,1-bis(4-methylphenyl)ethyl]-4-[1-(4-hydroxyphenyl)isopropyl]benzene, bis(4-hydroxy-2,3,5-trimethylphenyl)-2-hydroxyphenylmethane, bis(4-hydroxy-3,5-dimethylphenyl)-3,4-dihydroxyphenylmethane, 2,4-bis(3,5-dimethyl-4-hydroxyphenylmethyl)-6-methylphenol, and 4,6-bis[1-(4-hydroxyphenyl)isopropyl]resorcinol.
The amount of the ingredient (C), if any, in the composition of the present invention is preferably from 10% to 60% by weight and more preferably from 20% to 50% by weight, relative to the weight of the ingredient (A).
Where necessary, the composition of the present invention may further comprise any of compatible additives such as ultraviolet absorbents for inhibition of halation and surfactants for prevention of striation within ranges not adversely affecting the objects of the invention. Such ultraviolet absorbents include, for example, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxybenzophenone, 4-dimethylamino-21,41-dihydroxybenzophenone, 5-amino-3-methyl-l-phenyl-4-(4-hydroxyphenylazo)pyrazole, 4-dimethylamino-4xe2x80x2-hydroxyazobenzene, 4-diethylamino-4xe2x80x2-ethoxyazobenzene, 4-diethylaminoazobenzene, and curcumin. The surfactants include, but are not limited to, Fluorad FC-430 and FC-431 (trade names, available from Fluorochemical-Sumitomo 3M Co.), EFTOP EF122A, EF122B, EF122C and EF126 (trade names, available from Tohkem Products Corporation) and other fluorine-containing surfactants.
The positive photoresist composition of the present invention is preferably used as a solution prepared by dissolving each of the ingredients (A) and (B), as well as the ingredient (C) and other additional ingredients added according to necessity, in an appropriate solvent. Such solvents include those conventionally used in positive photoresist compositions, such as acetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, 2-heptanone, and other ketones; ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol monoacetate, propylene glycol monoacetate, diethylene glycol monoacetate, and monomethyl ethers, monoethyl ethers, monopropyl ethers, monobutyl ethers and monophenyl ethers of these compounds, and other polyhydric alcohols and derivatives thereof; dioxane and other cyclic ethers; and ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, and other esters. Each of these solvents can be used alone or in combination. Of these solvents, preferred solvents are acetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, 2-heptanone and other ketones; and ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate and other esters.
The positive photoresist composition of the present invention is preferably used in practice, for example, in the following manner: Each of the ingredients (A) and (B), as well as the ingredient (C) and other additional ingredients added according to necessity, is dissolved in an appropriate solvent as mentioned above to yield a coating solution; the coating solution is then applied, using a spinner or the like, onto a substrate such as a silicon wafer or a substrate having an antireflection coating, and is then dried to form a photosensitive layer; next, the photosensitive layer is irradiated and is exposed with i-line light through a desired mask pattern; and the exposed portions of the photosensitive layer are then dissolved and removed by dipping the substrate in a developer solution, for example, an alkaline aqueous solution such as a 1% to 10% by weight tetramethylammonium hydroxide (TMAH) aqueous solution, thus forming an image being in exact accordance with the mask pattern.